Superexchange interaction ( Lecture note on solid state physics )

Abstract:

In this note, we discuss the development of various interactions between magnetic ions; such as direct exchange interaction and superexchange interaction. Direct exchange involves an overlap of electron wavefunctions from the two sites and Coulomb electrostatic interaction repulsion. The Pauli exclusion principle keeps the electrons with parallel spin away from each other, thereby reducing the Coulomb repulsion. Originally superexchange acquired its name because of the relatively large distances, occupied by normally diamagnetic ions, radicals, or molecules. Small exchange coupling existed even between 3d ions separated by one negative ion. Anderson (1959) considered a molecular orbitals formed of the admixture of the localized 3d orbitals and p orbitals of the intervening negative ion. The bonding orbital is mainly occupied by a negative ion, while the antibonding orbital is partially occupied by 3d electrons, leading to the magnetism of the system. Thus the wavefunction of localized d spins extends over the neighboring negative ion. There is a probability of transferring from one 3d orbital of the magnetic ion to the neighboring 3d orbitals, leading to the exchange interaction.

To download the file click on the link below:

http://www.binghamton.edu/physics/docs/super-exchange.pdf